Inhibition of the enzyme nicotinamide phosphoribosyltransferase (NAMPRT) results in the inhibition of NF-kB, the inhibition of NF-kB being a result of the lowering of cellular concentrations of nicotinamide adenine dinucleotide (NAD) (Beauparlant et al (2007) AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics, 2007 Oct. 22-26 Abstract nr A82; and Roulson et al (2007) AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics, 2007 Oct. 22-26 Abstract nr A81). Tumor cells have elevated expression of NAMPRT and a high rate of NAD turnover due to high ADP-ribosylation activity required for DNA repair, genome stability, and telomere maintenance making them more susceptible to NAMPRT inhibition than normal cells. This also provides a rationale for the use of compounds of this invention in combination with DNA damaging agents for future clinical trials.
The pathways of NAD biosynthesis are shown in FIG. 1.
NAMPRT is involved in the biosynthesis of nicotinamide adenine dinucleotide (NAD) and NAD(P). NAD can be synthesized in mammalian cells by three different pathways starting either from tryptophan via quinolinic acid, from nicotinic acid (niacin) or from nicotinamide (niacinamide).
Quinolinic acid reacts with phosphoribosyl pyrophosphate to form niacin mononucleotide (dNAM) using the enzyme quinolinic acid phosphoribosyltransferase  which is found in liver kidney and brain.
Nicotinic acid (niacin) reacts with PRPP to form niacin mononucleotide (dNAM), using the enzyme niacin phosphoribosyltransferase  which is widely distributed in various tissues.
Nicotinamide (niacinamide) reacts with PRPP to give niacinamide mononucleotide (NAM) using the enzyme nicotinamide phosphoribosyltransferase (NAMPRT)  which is also widely distributed in various tissues.
The subsequent addition of adenosine monophosphate to the mononucleosides results in the formation of the corresponding dinucleotides: Niacin mononucleotide and niacinamide mononucleotide react with ATP to form niacin adenine dinucleotide (dNAD) and niacinamide adenine dinucleotide (NAD) respectively. Both reactions, although they take place on different pathways, are catalysed by the same enzyme, NAD pyrophosphorylase .
A further amidation step is required to convert niacin adenine dinucleotide (dNAD) to niacinamide adenine dinucleotide (NAD) The enzyme which catalyses this reaction is NAD synthetase . NAD is the immediate precursor of niacinamide adenine dinucleotide phosphate (NAD(P)) The reaction is catalysed by NAD kinase. For details see, e.g., Cory J. G. Purine and pyrimidine nucleotide metabolism In: Textbook of Biochemistry and Clinical Correlations 3rd edition ed. Devlin, T, Wiley, Brisbane 1992, pp 529-574.
Normal cells can typically utilize both precursors niacin and niacinamide for NAD(P) synthesis, and in many cases additionally tryptophan or its metabolites. Accordingly, murine glial cells use niacin, niacinamide and quinolinic acid (Grant et al. (1998) J. Neurochem. 70: 1759-1763). Human lymphocytes use niacin and niacinamide (Carson et al (1987) J. Immunol. 138: 1904-1907; Berger et al (1982) Exp. Cell Res. 137; 79-88). Rat liver cells use niacin, niacinamide and tryptophan (Yamada et al (1983) Int. J. Vit. Nutr. Res. 53: 184-1291; Shin et al (1995) Int. J. Vit. Nutr. Res. 65: 143-146; Dietrich (1971) Methods Enzymol. 18B; 144-149). Human erythrocytes use niacin and niacinamide (Rocchigiani et al (1991) Purine and pyrimidine metabolism in man VII Part B ed. Harkness et al Plenum Press New York pp 337-3490). Leukocytes of guinea pigs use niacin (Flechner et al (1970), Life Science 9: 153-162).
NAD(P) is involved in a variety of biochemical reactions which are vital to the cell and have therefore been thoroughly investigated. The role of NAD(P) in the development and growth of tumours has also been studied. It has been found that many tumour cells utilize niacinamide for cellular NAD(P) synthesis. Niacin and tryptophan which constitute alternative precursors in many normal cell types cannot be utilized in tumour cells, or at least not to an extent sufficient for cell survival. Selective inhibition of an enzyme which is only on the niacinamide pathway (such as NAMPRT) would constitute a method for the selection of tumour specific drugs. This has been exemplified by the NAMPRT inhibitor APO866. (see Hasmann and Schemainda, Cancer Res 63(21):7463-7442.)
It is known that various derivatives of 3,4-diamino-cyclobut-3-ene-1,2-dione, substituted in a specific manner have pharmacologically useful properties. In particular, certain derivatives are known to possess antiproliferative activity. All of these compounds however are structurally dissimilar from the compounds of the present invention.
Compounds comprising 3,4-diamino-cyclobut-3-ene-1,2-dione moieties are described in the following publications:
Use as potassium channel openers: J. Med. Chem. (2000) 43:1187, J. Med. Chem. (2000) 43: 1203, WO 02/062761.
Use as smooth muscle relaxants: WO 96/15103, WO 96/14300, WO 95/14005, U.S. Pat. No. 5,532,245.
Use as chemokine receptor binders: WO 02/083624.
Use as integrin receptor binders WO 00/035864, U.S. Pat. No. 6,420,396, WO 01/47867, WO 02/04426, WO 02/10136, WO 02/42264, U.S. Pat. No. 6,677,360.
Use as anticancer agents: WO 02/083624, EP 1674457 A1.